Abstract: A process for the selective recovery of precious metals from a medium loaded with precious metals and base metals. The selective recovery of precious metals is achieved by exposing the medium to an aqueous solution containing a complex of formula MX2—, wherein M is a metal of group IB or IIB of the Periodic Table of Elements, and X is a monovalent radical. A second invention relates to the removal of copper from the medium whereby elution of copper is achieved by exposing the medium to an aqueous solution capable of oxidising Cu(I) to Cu(II) whilst not eluting precious metals from the medium.

Abstract: Methods for preparing colloidal metal nanoparticles, in which seed colloids are added to a solution of reductant mixed with a solution containing a source of metal ions, include a method in which the seeds are colloidal gold nanoparticles, the source of gold ions is HAuCl4, and the reductant is NH2OH. SERS substrates are prepared by combining a colloidal gold monolayer with a solution containing a source of metal ions and a reductant such as NH2OH.

Abstract: A process for the recovery of gold and the platinum group metals from sources that contain relatively low amounts of the metals is described. The process is environmentally acceptable and uses no expensive and potentially dangerous organic solvents.

Abstract: Methods for preparing colloidal metal nanoparticles, in which seed colloids are added to a solution of reductant mixed with a solution containing a source of metal ions, include a method in which the seeds are colloidal gold nanoparticles, the source of gold ions is HAuCl4, and the reductant is NH2OH. SERS substrates are prepared by combining a colloidal gold monolayer with a solution containing a source of metal ions and a reductant such as NH2OH.

Abstract: Disclosed and claimed are efficient methods for leaching minerals from ores using an acidic solution such as sulfuric acid. Additional factors which can improve mineral recovery include the use of an alkali metal halide, grinding the ore, addition of a carbon source, and/or, adjustment of the temperature at which the process is carried out. Minerals such as titanium, iron, nickel, cobalt, silver and gold may be recovered by the methods of the present invention.

Abstract: A method of recovering precious metals from metal alloys produced aluminothermically from base metal smelter slag, includes treating the metal alloy with aqueous sulphuric acid solution having a pH of not greater than about 2 to cause dissolution of nickel and/or cobalt and iron and to cause formation of hydrogen sulfide which reacts with copper in the metal alloy to form a copper sulfide precipitate containing at least one precious metal, and separating the copper sulphide precipitate containing at least one precious metal from the remaining solution containing cobalt sulphate and/or nickel sulphate and ferrous sulphate.

Abstract: A process for the recovery of gold and the platinum group metals from sources that contain relatively low amounts of the metals is described. The process is environmentally acceptable and uses no expensive and potentially dangerous organic solvents.

Abstract: An organic acid salt is deposited on the surface of a solder powder containing Sn and Zn. Alternatively, 0.5 to 10 wt. % of a nonionic surfactant is added to a flux. By a method comprising such a procedure, provided are a lead-free solder powder and solder paste having good soldering characteristics wherein the reaction of an activating component with an alloy component in a flux is suppressed.

Abstract: A method for winning the valuable metal content of a leaching solution acidified with sulphuric acid, by solvent extraction and electrowinning and a following final product winning stage, for instance an electrowinning stage, wherein the pH of the leaching solution is raised successively to precipitate out the iron and arsenic present in a first precipitation stage, removing said first precipitate, and precipitating the valuable metal content of the leaching solution substantially totally in a following precipitation stage. The resultant precipitate containing valuable metal and gypsum is removed and leached in an acid environment to re-dissolve the valuable metal content, and the thus formed acid solution and its metal content are delivered to a solvent extraction circuit in which the metal content is converted to a substantial degree to an acid electrolyte from which metal or some other end product is won.

Abstract: A method is described for the preparation of platinum wherein first an aqueous solution of a hexahalogenoplatinate is passed through a cation exchanger and then the solution obtained, at a temperature T>+30° C. and a pH of 0 to 4, is reduced by a reducing agent to precipitate in the form of a platinum sponge.

Abstract: A paste to be fired at a temperature lower than melting point of silver for forming a circuit board comprising surface-modified silver powder consisting essentially of metal silver particles having an average particle size of not more than 10 &mgr;m and at least one member selected from the group consisting of oxides and double oxides containing at least one metal element selected from the group consisting of those belonging to Groups 2 to 14 of Periodic Table whose atomic number falls within the range of from 12 to 82, which is adhered to the surface of the individual metal silver particles. The surface-modified silver powder has an elevated sintering-initiation temperature and a reduced rate of heat shrinkage due to sintering. Therefore, the surface-modified silver powder is particularly suitable for use in making a circuit board, in particular an LTCC circuit board.

Abstract: A method for refining noble metals has a silver treating process including a nitric acid leaching step of silver, a purification step of the leaching solution, an electrolytic decomposition step of silver, and a recycling step after the electrolytic decomposition, wherein in the purification step, lime is added in order to precipitate the metallic impurities, such as selenium, tellurium, bismuth, and copper, by neutralization of the leaching solution, and in the recycling step, sulfuric acid is added to the solution after electrolytic decomposition to regenerate nitric acid for recycling use by precipitation of calcium in the solution as gypsum. Preferably, the refining method has a gold recovery process, as well as the silver treating process, wherein the residue of the nitric leaching of the crude silver is dissolved by chlorination and gold is recovered from the leaching solution by solvent extraction or reductive precipitation.

Abstract: A method for the chemical precipitation of metallic silver powder employs a two solution technique in which a solution of a tin salt and a solution a silver salt are mixed in the presence of an inorganic or organic acid, alumina, an anionic surfactant, and a colloid to form a precipitation solution at a temperature and pH suitable to effect the chemical precipitation of silver. Almost 80% by weight of the precipitated powder agglomerate is less than 25 .mu.m in diameter, and the individual powder particles which compose the agglomerate range in size from 0.2 to 2.0 .mu.m. In addition to the favorable size distribution, silver particles precipitated in the presence of a gelatin colloid can be used with a minimal amount of sieving so that little work hardening is imparted to the particles. The powder can be annealed at a temperature of up to 750.degree. C.

Abstract: A new method of creating thin free-standing pin hole-free hydrogen-selective palladium-bearing membranes that comprises thinning cold-rolled membranes by chemical etching or electrochemically electrolyzing of at least one membrane surface, and novel membranes produced thereby and including membranes with selected portions only thereof so thinned.

Abstract: A process and system and for extracting and refining gold from ores using relatively benign and inexpensive chemicals, fewer process steps, and permitting the recycling and re-use of process chemicals. The invention is preferably implemented as a two part process. In a first part process, gold is extracted from the ore and dissolved in a chemical solution to form a gold complex. The chemical solution preferably includes a KI and I.sub.2. Optionally, Isopropyl alcohol is mixed with the KI and I.sub.2 to serve as an accelerate. In a second part process, the complex is reduced to gold from the solution, preferably by one of two methods. The first method precipitates the gold complex by washing and decomposing of the gold complex to form pure gold. The second method electrolytically plates the gold from the gold complex solution onto a cathode to obtain pure gold.

Abstract: A method comprising the steps of solvent extracting a gold bearing chlorination leach solution with DBC, scrubbing the resulting gold bearing organic phase with hydrochloric acid and reducing gold is capable of recovering gold in high purity by:(1) adjusting the concentration of hydrochloric acid in the gold bearing chlorination leach solution to 0.5-1.75 N before the solvent extraction and then scrubbing the resulting gold bearing organic phase with 0.25-0.75 N hydrochloric acid; and/or(2) performing five-stage scrubbing with hydrochloric acid by either one of the following three approaches: i) after three-stage scrubbing, centrifugal separation is effected and separation is then performed by filtration with a filter having an opening size of 0.05-5 .mu.m, with the resulting organic phase being then subjected to two-stage scrubbing; ii) after five-stage scrubbing, centrifugal separation is effected and separation is then performed by filtration with a filter having an opening size of 0.05-5 .mu.

Abstract: An electrochemical apparatus and system for extracting and recovering metals from their compounds using electrochemical cells where the anolyte 10 is connected electrically to the catholyte 11 through an independent set of electrodes 13, 14 immersed in each electrolyte and connected to each other by a conductor 16. The specification details the application of this principle to commercial size cells and systems to extract metals from solutions, from ores in-situ, from ores in heaps and fixed beds, from fine metal concentrates dissolved either at the anode cell or in a separate leaching vessel. Alkaline electrolytes are also given for the extraction and recovery of nickel and copper from their oxide ores. A method for extracting gold from ores or residues is also included.

Abstract: There is provided a process for converting a silver-mercapto-s-triazine precipitate to a solid containing silver and a solution containing mercapto-s-triazine by contacting the silver-mercapto-s-triazine precipitate with one or more reducing agents. In preferred embodiments, at least one of the reducing agents has a redox potential more negative than about -0.9 V vs. Normal Hydrogen Electrode, NHE.

Abstract: The invention relates to a method of preparing a dental amalgam that is devoid of harmful free mercury, to be used as a filler for dental cavities. In particular the invention relates to processes by which two separate compositions characterized as treated silver and silver-mercury compound are formed, which are then used in a mixture with mercury to form the dental amalgam.

Abstract: A method for the manufacture of finely divided silver particles comprising the sequential steps:A. Forming an unsaturated solution of thermally decomposable silver-containing compound in a volatilizable solvent;B. Forming an aerosol from the unsaturated solution and a carrier gas;C. Heating the aerosol to a temperature above the decomposition temperature of the silver compound, but below the melting point of silver metal by which the silver compound is decomposed to form finely divided particles of pure densified silver; andD. Separating the precipitated silver particles from the carrier gas, reaction by-products and solvent voltilization products.

Abstract: Silver powder with a controlled surface area is made by introducing a silver ion containing solution and a mixed solution containing reducing agents and surfactants into a low temperature tank of 5.degree.-20.degree. C. and holding for a period of 7-60 minutes, followed by introducing the resulting reaction solution into a high temperature tank and holding further. The rest potential of the reaction solution is monitored to determine the end point of the reaction.

Abstract: There is disclosed a process useful for the extraction of gold, silver, and the platinum metals from precious metal containing ores which poses no threat to the environment or the ground water. The process utilizes sodium bromide, sodium chloride, and potassium monopersulfate to react with a water slurry of the precious metal containing ore which has been reduced to a minimum particle size of 250 mesh. The leaching out of the gold, silver, and the platinum metals occurs when the oxidation-reduction potential is maintained at +600 to +900 with the pH at 3.2 to 3.6. After the precious metals have been dissolved into solution, the ore tailings are filtered and discarded. The pregnant leach liquor is pumped to a holding tank where it is subsequently reacted with a solution of sodium hydroxide and sodium borohydride at a pH of 8.2 to 8.6 and the oxidation-reduction parameter held at -550 to -650.

Abstract: A method for the preparation of finely divided, dense packing, spherical shaped silver particles comprising the sequential steps of:(1) reacting an aqueous mixture of a silver salt with an alkanolamine to form a homogeneous aqueous solution of a dissolved silver alkanolamine complex;(2) preparing an aqueous solution of a reducing agent and, optionally, an alkanolamine; and(3) mixing together the silver alkanolamine complex solution and the reducing agent alkanolamine solution at a buffered pH and a temperature of 10.degree. C. to 100.degree. C. to form finely divided spherical silver particles.

Abstract: A process for recovering at least one precious metal from an ore containing carbonaceous material is disclosed. The process involves the use of certain plant derived ortho-quinone containing components, in particular, certain lignin and/or tannin derived components containing ortho-quinone functionality.Preferred compositions comprise at least one ligno sulfonate component containing ortho-quinone functionality. In the process, the use of at least one additional oxidant capable of maintaining the ortho-quinone containing functionality in the desired oxidation state provides for integrated process synergy.

Abstract: A process for recovering at least one precious metal from an ore containing metal sulfide material is disclosed. The process involves the use of promoting amounts of certain plant derived ortho-quinone containing components, in particular, certain lignin and/or tannin derived components containing ortho-quinone functionality. Preferred compositions comprise at least one ligno sulfonate component containing ortho-quinone functionality. In the process, the use of at least one additional oxidant capable of maintaining the ortho-quinone containing functionality in the desired oxidation state provides for integrated process synergy.

Abstract: Gold and silver are extracted from their elemental state or from complex ores and alloys by leaching them with a solution containing ammonia, ammonium salts and one or more oxidants. The process is particularly effective for refractory gold ores including sulfide and carbonaceous ores.

Abstract: A method is disclosed for the direct recovery of platinum group metals (PGM) from thiourea solutions or highly acidic aqueous solutions in general, such as leach solutions resulting from the acid leaching of precious metal bearing material. The method comprises reduction precipitation of the PGM from solution by alkali metal borohydride (preferably sodium or potassium borohydride) addition thereto at ambient temperature and pressure. The resulting precipitate is readily filtrable to give a product comprising high purity platinum group metal powder. The barren solution can be recycled to the upstream process.

Abstract: A process is disclosed for the direct and selective recovery of gold and/or silver from carbonate solutions, such as sodium carbonate which is used as an eluant for gold in a carbon-in-pulp process (CIP). The process comprises reduction precipitation of gold and/or silver from a carbonate solution having a pH in the alkaline range by the addition of stabilized alkali metal borohydride, such as sodium borohydride. The resulting gold and/or silver precipitate is generally of high purity and readily separated by filtration. The barren solution is in a condition such that it can be recycled to the upstream process.

Abstract: A process for the separation of rhodium from rhodium containing organic solutions, organic-aqueous mixtures or aqueous solutions containing complexing agents is disclosed. Metallic bismuth, bismuth oxide, bismuth hydroxide or another reducible bismuth compound is added to 50.degree. to 250.degree. C. as a precipitating agent, optionally with a reducing agent, and the precipitate is separated. The corresponding antimony compounds can also be used in place of bismuth.

Abstract: A process for recycling hydrogen cyanide from a cyanide-containing slurry is provided. The process includes the steps of adjusting the pH of a cyanide-containing slurry, volatilizing HCN contained in the pH adjusted slurry and contacting the volatilized HCN with a precious metals-containing slurry to recover precious metals therefrom. Alternatively, the HCN can be contacted with reclaim, or decant, water to recover cyanide, thereby conserving resources.

Abstract: A process is disclosed for the direct recovery of gold from thiourea, thiocyanate or thiosulfate solutions or acidified thiourea leach liquor. The process comprises reduction precipitation of the gold from solution by the addition of stabilized alkali metal borohydride, preferably sodium or potassium borohydride, at ambient temperature and pressure. The resulting gold precipitate is generally of high purity and is readily separated by filtration. The barren solution is in a condition such that it can be recycled to the upstream process.

Abstract: A reductive process for making finely divided silver particles in which the silver particles are precipitated from an aqueous acid solution of silver salt containing silica sol.

Abstract: A process is disclosed for the direct recovery of gold from cyanide leach liquor, thiourea leach liquor or Bio-D leach liquor. The process comprises reduction precipitation of the gold from solution by the addition of stabilized alkali metal borohydride, preferably sodium, potassium, lithium or ammonium borohydride, at ambient temperature and pressure. High purity gold is obtained by heating the reduced precipitate to about 1200.degree. C. The barren solution is in a condition such that it can be recycled to the upstream process.

Abstract: Aqueous iodine-iodide etching solutions are employed in the recovery of precious metals. Elemental iodine is precipitated from spent etching solutions and used to supply both the iodine and iodide of new etching solutions. Prior to extraction of the elemental iodine, used solutions, if not substantially contaminated, may be oxidized and recycled for further precious metal recovery. Aqueous etching solutions of hydriodic acid and iodine, or of ammonium iodide and iodine may be employed. Etching in such solutions, as well as in solutions of iodine and an alkali metal iodide, such as potassium iodide, may be accelerated by the use of small amounts of hydrogen peroxide (or equivalents) during etching.

Abstract: Heavy metal ions react with ferrous dithionite in acidic aqueous solution. They are reduced to metallic particles that are suitable for recycling and reuse when recovered from the acidic water. When chelating agents are present, they are deactivated by bonding to the ferrous ions. Ferrous dithionite, (FeS.sub.2 O.sub.4) is either generated in-situ or ferrous ions and dithionite ions can be provided by other methods.

Abstract: Gold and silver are extracted from their elemental state or from complex ores and alloys by leaching them with a solution containing ammonia, ammonium salts and one or more oxidants. The process is particularly effective for refractory gold ores including sulfide and carbonaceous ores.

Abstract: A process for adsorbing gold from a leach pulp by means of activated carbon is described in which the leach pulp (the leach solution together with the subdivided gold bearing ore) is diluted to a specific gravity of less than that of the activated carbon and is subsequently passed upwardly through a multistage liquid/solid contacting column. The contacting column is of the type having perforated plates or trays defining a series of vertically adjacent stages and the operation of the column has a cycle which includes a first part during which upward flow of diluted pulp fluidizes the activated carbon, a second part in which the carbon is allowed to settle on the trays and a third part during which a reverse flow of diluted pulp carries carbon downwardly through the column from one stage to another. In the third part of the cycle, loaded carbon is removed from the lowermost stage and treated to recover adsorbed gold therefrom.

Abstract: A reductive process for making finely divided silver particles in which the silver particles are precipitated from an aqueous acidic solution of silver salt, gelatin and alkyl acid phosphate.